1. Field of the Invention
This invention relates to mineral wool products to be used for the cultivation of plants, a method for manufacturing such a product as well as the use of this product for cultivating soilless grounds, particularly roofs, requiring extensive irrigation.
2. BACKGROUND OF THE PRIOR ART
Apart from the fibering process, an important stage in the production of mats with mineral fiber base is the production of the mat as such. In a well-known method, the molten glass is drawn into fibers for example by a centrifuging fiber forming process and an aqueous composition of binding agent based on a thermosettable resin is sprayed onto the fibers which are then collected by a collection device consisting for example, of an endless gas and water-permeable conveyor belt. Vacuum boxes are placed under the endless belt in order to create a certain subpressure. Due to this gas/and water-permeability, the mixtures of the fibers, the large amounts of gas generated by the fibering by burners or especially by air-induction and the water sprayed on the fibers can be separated, the fibers remaining on the belt and the gas and water mixture being sucked off below the conveyor belt. The wet fiber mattress is carried by the conveyor to a conforming and binding polymerizing chamber wherein the binder is cured and the mattress is calibrated to form the mat.
The gas/water mixture is spoiled with particles of the binding agent and remnants of fibers and consequently, is then treated with water in a washer. This cleaning treatment runs through filters on which the solid matter is deposited. The water cleaned in this way is then reintroduced into the washer, fresh water being eventually added only for compensating possible evaporation.
In addition to the advantageous mechanical properties, the polymerized binder, generally a phenol formaldehyde or urea formaldehyde resin, confers to the mineral wool product hydrophobic properties, although the mineral wool itself has hydrophilic properties. Such hydrophobization is suitable for products used in the construction industry as heat and/or sound insulating means since high requirements must be fulfilled with respect to the water resistivity of this product.
If, however, the mineral wool product is to be used as a substrate for cultivation of plants in soilless culturing, it is necessary that the mineral wool product be able to adsorb water or aqueous nutritive solutions or take them up in capillary fashion so that the plant roots or even the seeds spread out on the mineral wool are sufficiently supplied with water and/or aqueous nutritive solutions. As the traditionally produced mineral wool products do not fulfill these requirements for hydrophilic qualities, it is therefor necessary to use suitable additives in order to achieve this desired property.
From European Patent 201426 it is known to impregnate mineral fibers bound with a thermosettable resin binder, which are to be processed into blocks of substrates for plant cultivation, with a non-ionic tenside based on ethylated fatty alcohols.
Moreover, from German DE 2057945, it is known to render mineral wool products water absorbing during the production process by applying a mixture of phenol formaldehyde or urea formaldehyde resin and a tenside to the fibers.
Hydrophilizing agents containing the known tensides have the disadvantage of creating flocculations mainly of phenol resins when using the water effluents cleaning system, which then lead to clogging of the filters. Such a hazard may lead to an undesired breakdown of the whole production line since both time and cost-intensive cleaning of the filters becomes necessary.
Apart from this difficulty, these hydrophilizing agents have the further disadvantage that, due to their tensides content, they are washed out of the mineral wool itself in the course of time. This means that the mineral wool products lose their hydrophilic qualities and, on account of the content of resin binder, become hydrophobic again. Moreover, the mineral wool products containing tensides can indeed be wetted more easily but the water is not adsorbed at the mineral wool or retained by it and due to the effect of the tensides, flows off immediately or evaporates at once so that it is available for plant cultivation for only a very short time.